Demodulator having automatic quadrature control function

ABSTRACT

A demodulator for automatically performing quadrature control in which there is no necessity for the modulator side to perform precision adjustment and deterioration in characteristics e.g., error rate is suppressed for long. The demodulator includes a quadrature controller fed with an in-phase component and a quadrature component output from the quadrature detecting unit to correct quadrature error between phases of in-phase and quadrature signals based on a quadrature error signal, an automatic gain controller AGC outputting in-phase and quadrature components of a demodulated signal corrected for amplitude errors by an amplitude error signal, an error detection unit fed with in-phase and quadrature components of the demodulated signal to output in-phase and quadrature components and polarity signals, an amplitude error detector outputting in-phase and quadrature components of the amplitude error to the AGC based on the in-phase and quadrature components and the respective polarity signals, and a quadrature error detection unit generating a quadrature error signal Qd based on the in-phase and quadrature components and the polarity signals to output the generated quadrature error signal to the quadrature controller.

FIELD OF THE INVENTION

[0001] This invention relates to a demodulator and, more particularly,to a demodulator for automatically correcting errors in a detectionsignal of a quadrature detected modulated signal in a digital radiocommunication system.

BACKGROUND OF THE INVENTION

[0002]FIG. 11 shows a typical structure of a conventional demodulator.Referring to FIG. 11, this demodulator includes a quadrature detectingunit 1, an automatic amplitude controller (AGC) 3, an error detectionunit 3 and an amplitude error detection unit 4.

[0003] An input modulated signal is assumed to have been modulated inaccordance with a quadrature modulation system, such as QPSK (quadraturephase shift keying) or QAM (quadrature amplitude modulation). Therespective quadrature components (channels) are termed an in-phasecomponent or channel (Ich) and a quadrature component or channel (Qch),respectively. A quadrature detecting unit 1 receives a quadraturemodulated signal, as an IF (intermediate frequency) signal, and outputsan output signal as baseband signals Ich1 and Ich2. Meanwhile, thequadrature detecting unit 1 is made up of a known detection circuit,such as a synchronous detector, a semi-synchronous detector, or a delaydetector.

[0004] The AGC 2 is fed with Ich2 and Qch2 and, using amplitude errorsignals Ai, Aq, fed from the amplitude error detection unit 4, correctsthe amplitude errors to output signals Ich3, Qch3 each having a regularamplitude.

[0005] The error detection unit 3 uses (receives) Ich3, Qch3, outputfrom the AGC 2, to output error signals Ei, Eq and polarity signals Di,Dq.

[0006] The amplitude error detection unit 4 uses the signals Ei, Eq, Diand Dq, output by the error detection unit 3, to output Ai and Aq asrespective amplitude error signals of Ich and Qch.

SUMMARY OF THE DISCLOSURE

[0007] However, there is much to be desired in the art and variousproblems have been encountered in the course of the investigationstoward the present invention. That is, it is not possible with theconventional demodulator shown in FIG. 11 to correct quadraturedeviation produced in modulation.

[0008] Recently, an analog IC devices, termed quadrature modulators, aremanufactured and marketed, such that there is now commercially availablesuch a device automatically performing quadrature adjustment of themodulator. However, this device cannot be said to be of high precision.In particular, the device cannot be said to cope with multi-valuemodulation system, such as QAM, such that, if this device is put toPractical use, the BER (bit error rate) tends to be lowered. Ultimately,the quadrature deviation in a modulator in the multi-valued modulationsystem has to be adjusted mainly by manual operations.

[0009] As described above, it is not possible in the conventionaldemodulators to correct the quadrature deviation produced at the time ofmodulation.

[0010] It was necessary to make manual analog adjustment except if ananalog quadrature modulator can be applied. So, a quadrature adjustmentprocess was required during device production etc., thus necessitatingredundant time and operating steps.

[0011] Moreover, the demodulation circuit, adjusted manually in ananalog fashion, is liable to degradation due to temperature or humidityof the analog components, while being liable to deterioration with lapseof time, resulting in that quadrature properties cannot be maintainedfor prolonged time.

[0012] Thus, if quadrature errors are produced on the modulator side,correction is not possible with the conventional demodulator so thatdemodulated signals (playback signals) such as shown in FIG. 8 areproduced, thus naturally deteriorating the characteristics such as errorrate.

[0013] In view of the above-described status of the art, it is an objectof the present invention to provide a demodulator which, by performingautomatic correction of quadrature errors in a digital fashion.

[0014] It is another object of the present invention, to provide ademodulator which renders it unnecessary to make precision adjustment onthe modulator side and which assures operational stability and highreliability without producing deterioration in characteristics such aserror rate for a prolonged time.

[0015] Further objects of the present invention will become apparent inthe entire disclosure.

[0016] According to an aspect of the present invention there is provideda demodulator which comprises;

[0017] a quadrature controller for correcting quadrature errors of asignal quadrature-detected by a quadrature detecting unit, and aquadrature error detection unit for detecting a quadrature error basedon an error signal detected as to in-phase and quadrature componentsfrom a demodulated signal output from an automatic gain controller fedwith an input signal corrected for quadrature errors as an output signalof the quadrature controller, to feed the detected quadrature error(signal) to the quadrature controller.

[0018] According to a second aspect of the present invention, there isprovided a demodulator which comprises;

[0019] (a) a quadrature detecting unit fed with and quadrature-detectinga quadrature modulated signal to output an in-phase component and aquadrature component;

[0020] (b) a quadrature controller fed with the in-phase component andthe quadrature component output from the quadrature detecting unit, thequadrature controller correcting a quadrature error between the in-phasecomponent and the quadrature component based on an input quadratureerror signal, and outputting the resulting signal;

[0021] (c) an automatic gain controller fed with the in-phase componentand the quadrature component output from the quadrature controller andoutputting signals corrected for amplitude errors based on the inputamplitude error signal as the in-phase component and the quadraturecomponent of a demodulated signal;

[0022] (d) an error detection unit detecting, from the in-phasecomponent and the quadrature component of the demodulated signal outputfrom the automatic gain controller, an in-phase component of the errorsignal and a polarity signal of the in-phase component of thedemodulated signal, and a quadrature component of the error signal and apolarity signal of the quadrature component of the demodulated signal;

[0023] (e) an amplitude error detection unit generating an in-phasecomponent and a quadrature component of an amplitude error signal basedon the in-phase component of the error signal output from the errordetection unit and the polarity signal of the in-phase component of thedemodulated signal, and on the quadrature component of the error signaland the polarity signal of the quadrature component of the demodulatedsignal, to output the generated in-phase and quadrature components ofthe amplitude error signal to the automatic gain controller; and

[0024] (f) a quadrature error detect ion unit generating a quadratureerror signal based on the in-phase component of the error signal and thepolarity signal of the in-phase component of the demodulated signal,both output from the error detection unit, and on the in-phase componentof the error signal and the Polarity signal of the quadrature componentof the demodulated signal to feed the generated quadrature error signalto the quadrature controller.

[0025] According to a third aspect of the present invention there isprovided a demodulator which comprises;

[0026] (a) a quadrature detecting unit fed with a quadrature modulatedsignal as an input signal to quadrature-detect the input signal tooutput in-phase and quadrature components of a regular amplitude;

[0027] (b) a quadrature controller fed with the in-phase and quadraturecomponents output from the quadrature detection unit to correct thequadrature error between Phases of the in-phase and quadraturecomponents, based on a quadrature error signal;

[0028] (c) an automatic gain controller fed with the in-phase andquadrature components output from the quadrature controller to outputsignals corrected for respective amplitude errors as in-phase andquadrature components of a demodulated signal;

[0029] (d) an error detection unit detecting an in-phase component of anerror signal and a polarity signal of the in-phase component of thedemodulated signal, and a quadrature component of the error signal and apolarity signal of the quadrature component of the demodulated signal,from the in-phase and quadrature components of the demodulated signaloutput from the automatic gain controller; and

[0030] (e) a quadrature error detection unit generating a quadratureerror signal based on the in-phase component of the error signal and thepolarity signal of the in-phase component of the demodulated signal, andthe quadrature component of the error signal and a polarity signal ofthe quadrature component of the demodulated signal, all output from theerror detection unit, to feed the generated quadrature error signal tothe quadrature controller.

[0031] Further aspects of the Present invention are disclosed in theclaims, particularly in the dependent claims.

[0032] In a fourth aspect, the quadrature controller comprises;

[0033] a first low-pass filter fed with the quadrature error signaloutput from the quadrature error detection unit to smooth out and outputthe quadrature error signal;

[0034] a first multiplier multiplying the quadrature component outputfrom the quadrature detecting unit with an output of the first low-passfilter; and

[0035] a first adder adding the in-phase component output from thequadrature detecting unit and an output of the first multiplier

[0036] the quadrature component output from the quadrature detectingunit being directly output, an output of the first adder being output asan in-phase component corrected for quadrature errors.

[0037] In a fifth aspect, the quadrature error detection unit comprises;

[0038] a second multiplier multiplying the in-phase component of theerror signal (Ei) output from the quadrature detecting unit with thepolarity signal (Dq) of the quadrature component of the demodulatedsignal;

[0039] a third multiplier multiplying the quadrature component of theerror signal (Eq) output from the quadrature detecting unit with thepolarity signal (Di) of the in-phase component of the demodulatedsignal; and

[0040] a second adder summing outputs of the second and thirdmultipliers;

[0041] an output signal of the second adder being output as thequadrature error signal (Qd).

[0042] In a sixth aspect, the automatic gain controller comprises;

[0043] a second low-pass filter smoothing out and outputting thein-phase component of the amplitude error signal output from theamplitude error detection unit;

[0044] a third low-pass filter smoothing out and outputting thequadrature component of the amplitude error signal output from theamplitude error detection unit;

[0045] a fourth multiplier multiplying the in-phase component outputfrom the quadrature controller as an input signal with an in-phasecomponent of the amplitude error signal smoothed out by the secondlow-pass filter, the fourth multiplier outputting the result ofmultiplication as the in-phase component of the demodulated signal; and

[0046] a fifth multiplier multiplying the quadrature component outputfrom the quadrature controller as an input signal with a quadraturecomponent of the amplitude error signal smoothed out by the thirdlow-pass filter, the fifth multiplier outputting the result ofmultiplication as the quadrature component of the demodulated signal.

[0047] In a seventh aspect, the automatic gain controller comprises;

[0048] a first absolute value computing circuit determining an absolutevalue of the in-phase component output from the quadrature controller;

[0049] a second absolute value computing circuit determining an absolutevalue of the quadrature component output from the quadrature controller;

[0050] a third adder adding together outputs from the first and secondabsolute value computing circuit;

[0051] a fourth low pass filter smoothing out an output of the thirdadder;

[0052] a sixth multiplier multiplying an in-phase component output fromthe quadrature controller with an output of the fourth low pass filter;and

[0053] wherein the quadrature component output from the quadraturecontroller is directly output as the quadrature component, and an outputof the sixth multiplier is output as the in-phase component of thedemodulated signal.

BRIEF DESCRIPTION OF THE DRAWINGS

[0054]FIG. 1 shows a structure of an embodiment of the presentinvention.

[0055]FIG. 2 shows a structure of an AGC according to an embodiment ofthe present invention.

[0056]FIG. 3 shows a structure of an LPF according to an embodiment ofthe present invention.

[0057]FIG. 4 shows a structure of an error detection unit according toan embodiment of the present invention.

[0058]FIG. 5 shows a structure of an amplitude error detection unitaccording to an embodiment of the present invention.

[0059]FIG. 6 shows a structure of quadrature error detection unitaccording to an embodiment of the present invention.

[0060]FIG. 7 shows a structure of quadrature controller according to anembodiment of the present invention.

[0061]FIG. 8 is a graph showing demodulated signals on occurrence ofquadrature deviation in QPSK modulation on an I-Q complex plane.

[0062]FIG. 9 shows a modified embodiment of the present invention.

[0063]FIG. 10 shows a structure of an AGC according to the modifiedembodiment of the present invention.

[0064]FIG. 11 shows a structure of a conventional demodulator.

PREFERRED EMBODIMENTS OF THE INVENTION

[0065] A preferred embodiment of the present invention is now explained.Referring to FIG. 1, a preferred embodiment of the demodulator of thepresent invention includes a quadrature detecting unit 1, a quadraturecontroller 6, and an automatic amplitude controller (AGC) 2 in thisorder of signal flow, and further a feed back circuitry comprising anerror detection unit 3, an amplitude error detection unit 4 andquadrature error detection unit 5. The quadrature detecting unit 1 isfed as an input signal with an intermediate frequency (IF IN) signal forquadrature-detecting the input signal to output an in-phase componentIch1 and a quadrature component Qch1. The quadrature controller 6 is fedwith an in-phase component and a quadrature component output from thequadrature detecting unit 1 to correct the quadrature error based onquadrature error signal Qd. The automatic gain controller AGC 2 is fedwith the in-phase and quadrature components Ich2, Qch2 output from thequadrature controller 6 to output signals, which are corrected forrespective amplitude errors by in-phase and quadrature components Ai, Aqof the amplitude error, as in-phase and quadrature components Ich3, Qch3of the demodulated signal. The error detection unit 3 is fed with thein-phase and quadrature components Ich2, Qch3 of the demodulated signaloutput from the automatic gain controller 2, and detects and outputs anin-phase component and a polarity signal Ei, Di of the error signal anda quadrature component and a polarity signal Eq, Dq of the error signal.The quadrature error detection unit 4 outputs an in-phase component anda quadrature component Ai, Aq of the amplitude error to the automaticgain controller 2 based on a polarity signal Di of the in-phasecomponent Ich3 of the demodulated signal and the in-phase component Eiof the error signal, and on a polarity signal Dq of the quadraturecomponent Qch3 of the demodulated signal and the quadrature component Eqof the error signal, Di, Dq, Ei and Eq being output by the errordetection unit 3. The quadrature error detection unit 5 generates aquadrature error signal Qd based on an in-phase component Ei and apolarity signal Di of the error signal and on a quadrature component Eqand polarity signal Dq of the error signal, Ei, Di, Eq and Dq beingoutput from the error detection unit 3, and outputs the quadrature errorsignal Qd to the quadrature controller 6. The quadrature error betweenphases of the in-phase component Ich and the quadrature component Qchgenerated at the time of modulation is corrected by the quadraturecontroller 6.

[0066] Referring to FIG. 7, the quadrature controller 6 includes a firstlow-pass filter 63 for smoothing the quadrature error signal Qd outputfrom the quadrature error detection unit, a first multiplier 62 formultiplying the quadrature component Qch1 output from the quadraturedetecting unit with an output of the first low-pass filter 63, and afirst adder 61 for adding the in-phase component Ich1 output from thequadrature detecting unit and an output of the first multiplier 62. Thequadrature component output from the quadrature detecting unit isdirectly output as Qch2, an output of the first adder 61 being output asan in-phase component Ich2 corrected for quadrature errors.

[0067] Referring to FIG. 6, the quadrature error detection unit 5includes a second multiplier 51 for multiplying an in-phase component ofan error signal (Ei) output from the error detection unit 3 with apolarity signal Dq of a quadrature component Qch3 of the demodulatedsignal, a third multiplier 52 for multiplying a quadrature component Eqof the error signal output from the error detecting unit 3 with apolarity signal Di of the in-phase component Ich3 of the demodulatedsignal, and a second adder 53 for summing outputs of the second andthird adders 51, 52, wherein an output of the second adder 53 is outputas a quadrature error signal (Qd).

[0068] Referring to FIG. 2, the automatic gain controller 2 includes asecond low-pass filter 24 for smoothing out an in-phase component Ai ofan amplitude error signal output from the amplitude error detection unit4; a third low-pass filter 23 for smoothing out a quadrature componentAq of the amplitude error signal output from the amplitude errordetection unit 4; a fourth multiplier 21 for multiplying the in-phasecomponent Ich2 output from the quadrature controller 6 with an in-phasecomponent Ai of the amplitude error signal smoothed out by the secondlow-pass filter 24 for outputting the result of multiplication as anin-phase component Ich3 of the demodulated signal; and a fifthmultiplier 22 for multiplying the quadrature component Qch2 output fromthe quadrature controller 6 with a quadrature component Aq of theamplitude error signal smoothed out by the third low-pass filter 23 foroutputting the result of multiplication as a demodulated quadraturesignal Qch3.

[0069] In a preferred embodiment, shown in FIG. 9, the demodulator ofthe present invent ion includes quadrature detecting unit 7 fed as aninput signal with an intermediate frequency signal IF IN forquadrature-detecting the input signal to output an in-phase componentIch1 and a quadrature component Qch1; a quadrature controller 6 fed withthe in-phase and quadrature components output from the quadraturedetecting unit 1 to correct the quadrature error based on quadratureerror signal Qd; an automatic gain controller 8 fed with the in-phaseand quadrature components Ich2, Qch2 output from the quadraturecontroller 6 to output signals corrected for respective amplitude errorsas in-phase and quadrature components Ich3, Qch3 of a demodulatedsignal; an error detection unit 3 fed with the in-phase and quadraturecomponents of the demodulated signal output from the automatic gaincontroller 8 to detect and output an in-phase component and its polaritysignal (Ei, Di) of the error signal and a quadrature component and itspolarity signal (Eq, Dq) of the error signal; and a quadrature errordetect ion unit 5 for generating a quadrature error signal Qd based onan in-phase component Ei and its polarity signal Di of the error signaloutput from the error detect ion unit 3 and on a quadrature component Eqand its polarity signal Dq of the error signal to output the quadratureerror signal Qd to the quadrature controller 6.

[0070] Referring to FIG. 10, the automatic gain controller 8 includes afirst absolute value computing circuit 82 for determining an absolutevalue of an in-phase component output from the quadrature controller; asecond absolute value computing circuit 83 for calculating an absolutevalue of a quadrature component Qch2 output from the quadraturecontroller 6; an adder 84 for summing an output value of the secondabsolute value computing circuit 83 with an output value of the firstabsolute value computing circuit 82; a fourth low-pass filter 85 forsmoothing an output of the adder 84; and a sixth multiplier 81 formultiplying the in-phase component Ich2 output from the quadraturecontroller with an output of the fourth low-pass filter 85. An outputQch2 of quadrature controller 6 is output directly as a quadraturecomponent Qch3 of the demodulated signal, while an output of the sixthmultiplier 81 is output as an in-phase component Ich3 of the demodulatedsignal.

[0071] [Preferred Embodiments]

[0072] For further explaining the preferred embodiments of the presentinvention, an example of the present invention is explained withreference to the drawings.

[0073]FIG. 1 shows a configuration of an embodiment of a demodulator ofthe present invention. Referring to FIG. 1, an embodiment of the Presentinvention includes a quadrature detecting unit 1, an AGC 2, an errordetection unit 3, an amplitude error detection unit 4, a quadratureerror detection unit 5, and a quadrature controller 6. It is assumedthat the input modulation signal has been modulated in accordance withthe quadrature modulation system, such as QPSK or QAM. For each of thequadrature components (channels), appellations of in-phase component(channel, Ich) and quadrature component (channel, Qch) are used.

[0074] The quadrature-detecting unit 1 demodulates input quadraturemodulated signals, as IF (intermediate frequency) signals, into basebandsignals Ich1 and Qch1. Meanwhile, the quadrature-detecting unit 1 ismade up of known detection circuits, such as a synchronous detectioncircuit, a sub (or quasi)-synchronous circuit and/or a delay detectioncircuit.

[0075] The quadrature controller 6 is fed with baseband signals Ich1,Qch1, output by the quadrature detecting unit 1, to output signals Ich2,Qch2, freed of quadrature errors, using a quadrature error signal Qdinput from the quadrature error detection unit 5.

[0076] The AGC 2 is fed with Ich2, Qch2 to output Ich3, Qch3, havingregular (or normal) amplitudes, using amplitude error signals Ai, Aqinput from the amplitude error detection unit 4.

[0077] The error detection unit 3 outputs error signals Ei, Eq andpolarity signals Di, Dq, using Ich3, Qch3, output from the AGC 2.

[0078] The amplitude error detection unit 4 outputs amplitude errorsignals Ai, Aq of Ich and Qch, respectively, using the outputs Ei, Eq,Di, Dq output by the error detection unit 3.

[0079] The quadrature error detection unit 5 outputs the quadratureerror signal Qd, using the outputs Ei, Eq, Di, Dq supplied from theerror detection unit 3.

[0080] Referring to the drawings, the structure of respective elementsof the demodulator are hereinafter explained.

[0081]FIG. 2 shows an illustrative structure of the AGC 2. Referring toFIG. 2, the AGC 2 is made up of multipliers 21, 22 and low-pass filters(LPFs) 23, 24. The AGC 2 performs amplitude control so that the signalsIch2, Qch2 output by the quadrature controller 6 will be at regularsignal point positions, using the amplitude error signals Ai, Aq, outputby the amplitude error detection unit 4, to produce modulated signalsIch3, Qch3.

[0082]FIG. 3 shows an illustrative structure of the LPFs 23, 24 of theAGC 2 and an LPF 63 contained in the quadrature controller 6. Referringto FIG. 3, the LPF is comprised of an integrator made up of a flip-flop232 operating as a delay element and an adder 231. That is, the currentsignal and a signal delayed by one clock by the flip-flop 23 are summedtogether by the adder 231 and latched and output by the flip-flop 232.

[0083]FIG. 4 shows an illustrative structure of the error detection unit3. Referring to FIG. 4, the error detection unit 1 is made up of signalpoint error detection units 31, 32. The signal point error detectionunits 31, 32 detect errors (deviations) from the regular signal pointpositions of the input signals Ich3, Qch3 to output error (deviation)signals Ei Eq.

[0084] If the input signals Ich3, Qch3 are deviated in the positive ornegative direction from the regular signal point positions, the outputerror signals Ei, Eq assume negative and positive values, respectively.Since the regular signal point positions vary with modulation systemsused, a signal MOD specifying the modulation system is supplied to thesignal point error detection units 31, 32. The polarity signals Di, Dqrepresent polarities of the signal Ich3, Qch3, respectively, and areacquired from respective sign bits.

[0085]FIG. 5 shows the structure of the amplitude error detection unit4. Referring to FIG. 5, the amplitude error detection unit 4 includes amultiplier 42 for multiplying the in-phase component Ei of the errorsignal and its polarity signal Di to output the amplitude error signalAi, and a multiplier 41 for multiplying the quadrature component Eq ofthe error signal and its polarity signal Dq to output an amplitude errorsignal Aq.

[0086]FIG. 6 shows the structure of the quadrature error detect ion unit5. Referring to FIG. 6, the quadrature error detection unit 5 is made upof multipliers 51, 52 and an adder 53. The results of multiplication ofEi with Dq and those of Eq with Di in the multipliers 51, 52 are summedtogether in the adder 53 to give a quadrature error signal Qd (see thefollowing equation (1)).

[0087]FIG. 7 shows the structure of the quadrature controller 6.Referring to FIG. 7, the quadrature controller 6 is made up of an adder61, a multiplier 62 and a low pass filter LPF 63.

[0088] The quadrature error signal Qd, output from the quadrature errordetection unit 5, is smoothed by the LPF 63, an output of which ismultiplied by the multiplier 62 with Qch1. The resulting product issummed (added) in the adder 61 with Ich1 (Ich1 less the product obtainedon multiplication) and the resulting sum is output as Ich2 to correctthe quadrature error. The output Qch2 on the Qch side is no other thanQch1.

[0089] The operation of an example of the Present invention is explainedmainly with reference to the quadrature controller 6.

[0090] The signal point error signals Ei, Eq, obtained by the errordetection unit 3, and the polarity signals Di, Dq, indicate whether thereproduced signal is deviated from the regular signal point position inthe positive direction or in the negative direction. For quadraturecontrol, these signals need to be converted into quadrature error(deviation) signals.

[0091]FIG. 8 shows on an I-Q complex plane the modulated signal in caseof occurrence of a quadrature deviation. It is seen from FIG. 8 that,since the distances between respective signal Points and the point oforigin are inherently equal to each other, the signal points should bepositioned on apex points of a square. However, these signal points areactually positioned on apex points of a diamond shape. In order tocorrect this state, such error signals, which will correct the deviationin the diagonal directions from the regular signal points, as shown inFIG. 8, are required.

[0092] For obtaining these error signals, it is only sufficient if thequadrature error signals Qd, represented by the following equation (1):

Qd=Ei·Dq+Eq·Di   (1)

[0093] is used.

[0094] The quadrature error detection unit 5 generates this Qd.

[0095] The quadrature error control based on quadrature error signals isexplained. Assume that the IF input signal to a quadrature detectionunit 7 is A (t), an angular velocity of a local oscillator, not shown,in the quadrature detection unit 7, is ω rad/sec and a quadrature erroris δ rad, the signals Ich, Qch input to an A/D (analog/digital)converter, not shown, supplying Ich1, Qch1 of digital signals to thequadrature controller 6, are given by the following equations (2) and(3):

Ich=A(t) cos (ωt+δ)

=A(t) cos ωt·cos δ−A(t) sin ωt·sin δ

=A(t) cos ωt·cos δ−Qch·sin δ  (2)

Qch=A(t)sin ωt   (3).

[0096] For demodulating this signal regularly, δ in Ich of the aboveequation (2) needs to be eliminated. However, the term of A(t) cosωt·cos δ represents merely a lowered gain of Ich and can be corrected byAGC2.

[0097] So, in the Ich of the above equation (2), it suffices if the termof—Qch·sin δ in Ich of the equation (2) is corrected.

[0098] Since δ may be regarded as a constant for a short period of time,the product of the quadrature error signal with the Qch value may besummed (added) to Ich to correct the quadrature error. In an embodimentof the present invention, the above-mentioned correction operation isperformed in the quadrature controller 6 shown in FIG. 7.

[0099] A further embodiment of the present invention is now explained.FIG. 9 shows a second embodiment of the present invention. Referring toFIG. 9, the second embodiment of the present invention differs from thefirst embodiment shown in FIG. 1 as to the quadrature detecting unit 7and the AGC 8.

[0100] In the above-described first embodiment, in which the AGC 2corrects the amplitudes of Ich and Qch, it is unnecessary for thequadrature-detecting unit 1 to output a signal of the regular amplitude.On the other hand, in the second embodiment of the present invention,the quadrature detecting unit 7 outputs signals of the regularamplitude. So, it is unnecessary for the AGC 8 to Perform the operationfor causing the output signal to be on the regular amplitude, such thatit is only necessary for the AGC 8 to correct the lowering of the gainof Ich that is not corrected by the quadrature controller 6.

[0101]FIG. 10 shows an illustrative structure of the AGC 8. Referring toFIG. 11, the AGC 8 is made up of a (sixth) multiplier 81, absolute valuecircuits (calculating units) 82, 83, an adder 84 and an (fourth) LPF 85.The absolute value circuits 82, 83 determine the amplitudes of Ich2 andQch2 and a relative magnitude (difference) thereof by the adder 84 toobtain an amplitude error signal between Ich and Qch. It is noted thatthe adder 84 operates as a subtractor for outputting a difference valuecorresponding to the output value of the absolute value circuit 83 lessthe output value of the absolute value circuit 82. The amplitude errorsignal obtained by the adder 84 is smoothed by the LPF 85. The smoothedamplitude error signal is multiplied by the Ich by the multiplier 81.The resulting product is output as Ich3. The Qch2 from the quadraturecontroller 6 is directly output as Qch3 to correct the ampitudedifference between Ich and Qch.

[0102] The meritorious effects of the present invention are summarizedas follows.

[0103] The present invention provides a configuration comprising aquadrature controller correcting quadrature errors of a signalquadrature-detected by a quadrature detecting unit, and a quadratureerror detecting unit detecting a quadrature error, wherein thequadrature errors are corrected based on an error signal detected as toin-phase and quadrature components of a demodulated signal output froman automatic gain controller fed as an input signal with an outputsignal of the quadrature controller, and the detected quadrature errorQd is fed to the quadrature controller. Therefore, it is unnecessary tomake manual adjustment of analog circuit elements such that quadratureerrors of the modulator can be eliminated fully digitally andautomatically. Moreover, the present invention gives a meritoriouseffects that full digitization facilitates designing as LSI.

[0104] It should be noted that other objects, features and aspects ofthe present invention will become apparent in the entire disclosure andthat modifications may be done without departing the gist and scope ofthe present invention as disclosed herein and claimed as appendedherewith.

[0105] Also it should be noted that any combination of the disclosedand/or claimed elements, matters and/or items might fall under themodifications aforementioned.

What is claimed is:
 1. A demodulator comprising: (a) a quadraturecontroller fed with a signal quadrature-detected by a quadraturedetecting unit as an input signal to correct a quadrature error betweenphases of an in-phase component and a quadrature component of saidsignal based on a quadrature error signal used for correcting saidquadrature error to output a corrected signal; (b) an error detect ionunit detecting an error signal between the in-phase component and thequadrature component of a demodulated signal output by an automatic gaincontroller fed with an output signal of said quadrature controllercorrected for quadrature error; and (c) a quadrature error detectionunit detecting the quadrature error based on said error signal to feedthe quadrature error signal to said quadrature controller.
 2. Ademodulator comprising: (a) a quadrature detecting unit fed with andquadrature-detecting a quadrature modulated signal to output an in-phasecomponent and a quadrature component; (b) a quadrature controller fedwith the in-phase component and the quadrature component output fromsaid quadrature detecting unit, said quadrature controller correctingthe quadrature error between the in-phase component and the quadraturecomponent based on an input quadrature error signal, and outputting theresulting signal; (c) an automatic gain controller fed with the in-phasecomponent and the quadrature component output from said quadraturecontroller and outputting signals corrected for amplitude errors basedon the input amplitude error signal as the in-phase component and thequadrature component of a demodulated signal; (d) an error detectionunit detecting, from the in-phase component and the quadrature componentof the demodulated signal output from said automatic gain controller, anin-phase component of said error signal and a polarity signal of thein-phase component of the demodulated signal, and a quadrature componentof the error signal and a polarity signal of the quadrature component ofsaid demodulated signal; (e) an amplitude error detection unitgenerating an in-phase component and a quadrature component of anamplitude error signal based on the in-phase component of said errorsignal output from said error detection unit and the polarity signal ofthe in-phase component of the demodulated signal, and on the quadraturecomponent of the error signal and the polarity signal of the quadraturecomponent of said demodulated signal, to output the generated in-phaseand quadrature components of said amplitude error signal to saidautomatic gain controller; and (f) a quadrature error detection unitgenerating a quadrature error signal based on the in-phase component ofthe error signal and the polarity signal of the in-phase component ofsaid demodulated signal, both output from said error detection unit, andon the in-phase component of said error signal and the polarity signalof the quadrature component of said demodulated signal to feed thegenerated quadrature error signal to said quadrature controller.
 3. Ademodulator comprising: (a) an quadrature detecting unit fed with aquadrature modulated signal as an input signal to quadrature-detect theinput signal to output in-phase and quadrature components of a regularamplitude; (b) a quadrature controller fed with the in-phase andquadrature components output from the quadrature detection unit tocorrect the quadrature error between phases of the in-phase andquadrature components, based a quadrature error signal; (c) an automaticgain controller fed with the in-phase and quadrature components outputfrom said quadrature controller to output signals corrected forrespective amplitude errors as in-phase and quadrature components of ademodulated signal; (d) an error detection unit detecting an in-phasecomponent of an error signal and a polarity signal of the in-phasecomponent of the demodulated signal, and a quadrature component of theerror signal and a polarity signal of the quadrature component of thedemodulated signal, from the in-phase and quadrature components of thedemodulated signal output from the automatic gain controller; and (e) aquadrature error detection unit generating a quadrature error signalbased on the in-phase component of the error signal and the polaritysignal of the in-phase component of the demodulated signal, and thequadrature component of the error signal and a polarity signal of thequadrature component of the demodulated signal, all output from saiderror detection unit, to feed the generated quadrature error signal tosaid quadrature controller.
 4. The demodulator as defined in claim 2wherein said quadrature controller comprises; a first low-pass filterfed with said quadrature error signal output from said quadrature errordetection unit to smooth out and output said quadrature error signal; afirst multiplier multiplying the quadrature component output from saidquadrature detecting unit with an output of said first low-pass filter;and a first adder adding the in-phase component output from saidquadrature detecting unit and an output of said first multiplier; thequadrature component output from said quadrature detecting unit beingdirectly output, an output of said first adder being output as anin-phase component corrected for quadrature errors.
 5. The demodulatoras defined in claim 3 wherein said quadrature controller comprises; afirst low-pass filter fed with said quadrature error signal output fromsaid quadrature error detection unit to smooth out and output saidquadrature error signal; a first multiplier multiplying the quadraturecomponent output from said quadrature detecting unit with an output ofsaid first low-pass filter; and a first adder adding the in-phasecomponent output from said quadrature detecting unit and an output ofsaid first multiplier; the quadrature component output from saidquadrature detecting unit being directly output, an output of said firstadder being output as an in-phase component corrected for quadratureerrors.
 6. The demodulator as defined in claim 2 wherein said quadratureerror detection unit comprises; a second multiplier multiplying thein-phase component of the error signal (Ei) output from said quadraturedetecting unit with the polarity signal (Dq) of the quadrature componentof said demodulated signal; a third multiplier multiplying thequadrature component of the error signal (Eq) output from saidquadrature detecting unit with the polarity signal (Di) of the in-phasecomponent of said demodulated signal; and a second adder summing outputsof said second and third multipliers; an output signal of said secondadder being output as said quadrature error signal (Qd).
 7. Thedemodulator as defined in claim 3 wherein said quadrature errordetection unit comprises; a second multiplier multiplying the in-phasecomponent of the error signal (Ei) output from said quadrature detectingunit with the polarity signal (Dq) of the quadrature component of saiddemodulated signal; a third multiplier multiplying the quadraturecomponent of the error signal (Eq) output from said quadrature detectingunit with the polarity signal (Di) of the in-phase component of saiddemodulated signal; and a second adder summing outputs of said secondand third multipliers, an output signal of said second adder beingoutput as said quadrature error signal (Qd).
 8. The demodulator asdefined in claim 2 wherein said automatic gain controller comprises; asecond low-pass filter smoothing out and outputting the in-phasecomponent of the amplitude error signal output from said amplitude errordetection unit; a third low-pass filter smoothing out and outputting thequadrature component of the amplitude error signal output from saidamplitude error detection unit; a fourth multiplier multiplying thein-phase component output from said quadrature controller as an inputsignal with an in-phase component of the amplitude error signal smoothedout by said second low-pass filter, said fourth multiplier outputtingthe result of multiplication as the in-phase component of thedemodulated signal; and a fifth multiplier multiplying the quadraturecomponent output from said quadrature controller as an input signal witha quadrature component of the amplitude error signal smoothed out bysaid third low-pass filter, said fifth multiplier outputting the resultof multiplication as the quadrature component of the demodulated signal.9. The demodulator as defined in claim 3 wherein said automatic gaincontroller comprises; a first absolute value computing circuitdetermining an absolute value of the in-phase component output from saidquadrature controller; a second absolute value computing circuitdetermining an absolute value of the quadrature component output fromsaid quadrature controller; a third adder adding together outputs fromthe first and second absolute value computing circuits; a fourth lowpass filter smoothing out an output of the third adder; a sixthmultiplier multiplying an in-phase component output from said quadraturecontroller with an output of the fourth low pass filter; and wherein thequadrature component output from the quadrature controller is directlyoutput as the quadrature component, and an output of the sixthmultiplier is output as the in-phase component of the demodulatedsignal.